This joint resolution of Congress (H.J. RES 1145) dated August 7, 1964, gave President Lyndon Johnson authority to increase U.S. involvement in the war between North and South Vietnam.

On August 4, 1964, President Lyndon Johnson announced that two days earlier, U.S.
ships in the Gulf of Tonkin had been attacked by the North Vietnamese. Johnson
dispatched U.S. planes against the attackers and asked Congress to pass a resolution
to support his actions. The joint resolution “to promote the maintenance
of international peace and security in southeast Asia” passed on August
7, with only two Senators (Wayne Morse and Ernest Gruening) dissenting, and became
the subject of great political controversy in the course of the undeclared war
that followed.

The Tonkin Gulf Resolution stated that “Congress approves and supports
the determination of the President, as Commander in Chief, to take all necessary
measures to repeal any armed attack against the forces of the United States
and to prevent any further aggression.” As a result, President Johnson,
and later President Nixon, relied on the resolution as the legal basis for their
military policies in Vietnam.

As public resistance to the war heightened, the resolution was repealed by
Congress in January 1971.